The processing of carbonaceous feedstocks (e.g. biomass) to produce chemicals and/or fuels can be accomplished by fast (rapid or flash) pyrolysis. Fast pyrolysis is a generic term that encompasses various methods of rapidly imparting a relatively high temperature to feedstocks for a very short time, and then rapidly reducing the temperature of the primary products before chemical equilibrium can occur. Using this approach, the complex structures of carbonaceous feedstocks are broken into reactive chemical fragments, which are initially formed by depolymerization and volatilization reactions. The non-equilibrium products are then preserved by rapidly reducing the temperature.
More recently, a rapid thermal process (RTP) has been developed for carrying out fast pyrolysis of carbonaceous material. The RTP utilizes an upflow transport reactor and reheater arrangement, and makes use of an inert inorganic solid particulate heat carrier (e.g. typically sand) to carry and transfer heat in the process. The RTP reactor provides an extremely rapid heating rate and excellent particle ablation of the carbonaceous material, which is particularly well-suited for processing of biomass, as a result of direct turbulent contact between the heated inorganic solid particulates and the carbonaceous material as they are mixed together and travel upward through the reactor. In particular, the heated inorganic solid particulates transfer heat to pyrolyze the carbonaceous material forming char and gaseous products including high quality pyrolysis oil, which are removed from the reactor by a cyclone. The cyclone separates the gaseous products and solids (e.g. inorganic solid particulates and char), and the solids are passed to the reheater.
The reheater is a vessel that burns the char into ash and reheats the inorganic solid particulates, which are then returned to the reactor for pyrolyzing more carbonaceous material. An oxygen-containing gas, typically air, is supplied to the reheater for burning the char. The inorganic solid particulates and char are contained in the lower portion of the reheater and are fluidized by the air, forming a fluidized bubbling bed also referred to as the dense phase. The reheater also has a dilute phase that is above the dense phase and comprises primarily flue gas, entrained inorganic solid particulates, and ash, which are the byproducts formed from combusting the char with the air. The flue gas, entrained inorganic solid particulates, and ash are removed from the reheater to a separation device which separates a portion of solids from the flue gas.
Currently, higher capacity RTP arrangements are desired that are capable of handling carbonaceous feedstock rates of up to about 400 bone dry metric tons per day (BDMTPD) or higher compared to previously lower feedstock rates of less than about 100 BDMTPD. The increased capacity results in more char being produced in the RTP reactor, and the RTP reheater and auxiliary equipment (e.g. cyclone, air blower, etc.) need to be larger in size to support the increased feedstock rate without producing excessive heat from burning the additional char. In particular, many newer RTP reheaters require additional volume to accommodate additional air supplied to the reheaters for cooling to control the otherwise rising temperatures from burning the additional char, and can have sizes of up to about 12 meters (m) or greater in diameter and heights of up to about 25 m or greater. Unfortunately, the larger sizes of these reheaters substantially increase the cost and complexity of shipping, installing, and operating the reheaters.
Accordingly, it is desirable to provide apparatuses and methods for controlling heat for rapid thermal processing that can adequately support higher carbonaceous feedstock rates without producing excessive heat in the reheater from burning the additional char which may, for example, exceed the design temperature of the equipment and limit the feed capacity. Moreover, it is also desirable to provide apparatuses and methods for controlling heat for rapid thermal processing without substantially increasing the cost and complexity of shipping, installing, and operating the reheaters. Furthermore, other desirable features and characteristics of the present invention will become apparent from the subsequent detailed description of the invention and the appended claims, taken in conjunction with the accompanying drawings and this background of the invention.